linux-kernel - [PATCH 43/44] kdbus: Give up on failed fd allocation

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Message-Id: <52bb93d53cbbfbeed6f6d34b7c9eb8aa224ed9b8.1444302968.git.sergei@s15v.net>
Date:	Thu,  8 Oct 2015 14:32:12 +0300
From:	Sergei Zviagintsev <sergei@...v.net>
To:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Daniel Mack <daniel@...que.org>,
	David Herrmann <dh.herrmann@...glemail.com>,
	Djalal Harouni <tixxdz@...ndz.org>
Cc:	linux-kernel@...r.kernel.org, Sergei Zviagintsev <sergei@...v.net>
Subject: [PATCH 43/44] kdbus: Give up on failed fd allocation

If we failed to allocate a file descriptor, do not try to do it again on
the next iteration. There are few chances that we will have success, and
we can simplify the algorithm assuming that valid fd numbers are not
mixed with -1 values.

Signed-off-by: Sergei Zviagintsev <sergei@...v.net>
---
 ipc/kdbus/message.c | 42 ++++++++++++++++++++++++------------------
 1 file changed, 24 insertions(+), 18 deletions(-)

diff --git a/ipc/kdbus/message.c b/ipc/kdbus/message.c
index da685049d66c..75e6213e7ed5 100644
--- a/ipc/kdbus/message.c
+++ b/ipc/kdbus/message.c
@@ -123,7 +123,7 @@ int kdbus_gaps_install(struct kdbus_gaps *gaps, struct kdbus_pool_slice *slice,
 {
 	bool incomplete_fds = false;
 	struct kvec kvec;
-	size_t i, n_fds;
+	size_t i, n_fds, n_memfds;
 	int ret, *fds;
 
 	if (!gaps) {
@@ -140,25 +140,31 @@ int kdbus_gaps_install(struct kdbus_gaps *gaps, struct kdbus_pool_slice *slice,
 	}
 
 	fds = kmalloc_array(n_fds, sizeof(*fds), GFP_TEMPORARY);
-	n_fds = 0;
 	if (!fds)
 		return -ENOMEM;
 
 	/* 1) allocate fds and copy them over */
 
+	n_fds = 0; /* n_fds now tracks the number of allocated fds */
 	if (gaps->n_fds > 0) {
 		for (i = 0; i < gaps->n_fds; ++i) {
 			int fd;
 
 			fd = get_unused_fd_flags(O_CLOEXEC);
-			if (fd < 0)
+			if (fd < 0) {
 				incomplete_fds = true;
+				break;
+			}
 
 			WARN_ON(!gaps->fd_files[i]);
 
-			fds[n_fds++] = fd < 0 ? -1 : fd;
+			fds[n_fds++] = fd;
 		}
 
+		/* If we couldn't allocate a fd, fill the rest with -1 */
+		for ( ; i < gaps->n_fds; ++i)
+			fds[i] = -1;
+
 		/*
 		 * The file-descriptor array can only be present once per
 		 * message. Hence, prepare all fds and then copy them over with
@@ -175,18 +181,18 @@ int kdbus_gaps_install(struct kdbus_gaps *gaps, struct kdbus_pool_slice *slice,
 			goto exit;
 	}
 
-	for (i = 0; i < gaps->n_memfds; ++i) {
+	n_memfds = 0;
+	for (i = 0; i < gaps->n_memfds && !incomplete_fds; ++i) {
 		int memfd;
 
 		memfd = get_unused_fd_flags(O_CLOEXEC);
 		if (memfd < 0) {
 			incomplete_fds = true;
-			fds[n_fds++] = -1;
 			/* memfds are initialized to -1, skip copying it */
-			continue;
+			break;
 		}
 
-		fds[n_fds++] = memfd;
+		fds[gaps->n_fds + n_memfds++] = memfd;
 
 		/*
 		 * memfds have to be copied individually as they each are put
@@ -208,21 +214,21 @@ int kdbus_gaps_install(struct kdbus_gaps *gaps, struct kdbus_pool_slice *slice,
 
 	/* 2) install fds now that everything was successful */
 
-	for (i = 0; i < gaps->n_fds; ++i)
-		if (fds[i] >= 0)
-			fd_install(fds[i], get_file(gaps->fd_files[i]));
-	for (i = 0; i < gaps->n_memfds; ++i)
-		if (fds[gaps->n_fds + i] >= 0)
-			fd_install(fds[gaps->n_fds + i],
-				   get_file(gaps->memfd_files[i]));
+	for (i = 0; i < n_fds; ++i)
+		fd_install(fds[i], get_file(gaps->fd_files[i]));
+	for (i = 0; i < n_memfds; ++i)
+		fd_install(fds[gaps->n_fds + i],
+			   get_file(gaps->memfd_files[i]));
 
 	ret = 0;
 
 exit:
-	if (ret < 0)
+	if (ret < 0) {
 		for (i = 0; i < n_fds; ++i)
-			if (fds[i] >= 0)
-				put_unused_fd(fds[i]);
+			put_unused_fd(fds[i]);
+		for (i = 0; i < n_memfds; ++i)
+			put_unused_fd(fds[gaps->n_fds + i]);
+	}
 	kfree(fds);
 	*out_incomplete = incomplete_fds;
 	return ret;
-- 
1.8.3.1

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